Bromodeoxyuridine (BrdU) treatment to measure hepatocellular proliferation does not mask furan-induced gene expression changes in mouse liver

Bromodeoxyuridine (BrdU) is a synthetic nucleoside used to detect cellular proliferation. BrdU incorporates in the place of thymine but pairs with guanine, thereby increasing the risk of transition mutations in dividing cells. Given its mutagenicity, standard practice is to use a second cohort of animals for parallel toxicogenomics studies; however, the impact of BrdU on global gene expression is unknown. To test this, we performed a case study to determine whether the molecular mode of action of furan, a liver carcinogen, could be detected in BrdU-treated samples. We measure global hepatic gene expression using Agilent DNA microarrays in female B6C3F1 mice that were sub-chronically exposed to 0, 1, 4, or 8 mg/kg bodyweight (bw) per day furan either in the presence (+BrdU) or absence (−BrdU) of BrdU. Exposure to 0.02% BrdU in drinking water for five days resulted in minimal gene expression changes. A comparison of +BrdU versus −BrdU control mice revealed only 11 probes with fold change ≥ 1.5 and false discovery rate (FDR) corrected p ≤ 0.05. The same comparison in the high dose group yielded only 3 differentially expressed probes. Differentially expressed gene lists generated for furan-treated versus control mice and were compared for the −BrdU and +BrdU groups. The high dose of furan had 452 shared probes and 27 and 90 unique probes for −BrdU and +BrdU groups, respectively. These differences did not impact hierarchical clustering. Further, they did not impair detection of the previously reported furan mode of action, which was well represented in the BrdU-treated samples. Taken together, we demonstrate that BrdU treatment does not mask important furan-induced transcriptional changes. We suggest that BrdU-treated mice could be used for toxicogenomic analysis, which would generally halve the number of rodents required for toxicogenomics studies. However, we also recommend that this type of case study be repeated for other chemicals before the use of BrdU-treated animals in omics studies becomes common practice.